The present invention is directed to a calibration apparatus for allowing the user of a DLco testing machine to check the ability of the machine to correctly measure carbon monoxide levels in a gas sample.
There are many different types of tests that are available to today""s medical practitioners and pulmonary rehabilitation practitioners for testing various functions of the lung. Many types of diseases, such as emphysema, and injuries reduce the ability of gasses to transfer across the membrane that separates the interior gas spaces of the lungs from the pulmonary-capillary system. This membrane is often referred to as the alveolar-capillary membrane.
A number of somewhat related tests have been developed in order to test the function of this membrane without invasion into the lung by surgery or apparatus. These non-invasive tests take advantage of the manner in which carbon monoxide transfers across the membrane and in general measure the rate at which carbon monoxide diffuses across the human lung. The rate of carbon monoxide diffusion then provides the testor with information as to diffusion of other gasses, especially oxygen and carbon dioxide. Because the carbon monoxide reacts in certain ways with the hemoglobin, concentrations of the carbon monoxide in the blood (at least at the levels utilized in testing) are not relevant and a practitioner can calculate the diffusion of carbon monoxide across the membrane by knowing such factors as the initial concentration of carbon monoxide in the lungs, an elapsed time, and the final concentration of the carbon monoxide after the elapsed time. Such tests allow the calculation of a gas transfer factor for carbon monoxide which is generally referred to as the pulmonary diffusing capacity (DLco). While one principal testing technique is used for determining this factor, other techniques have been used in the past, have been proposed or may be developed in the future.
Various types of machines have been developed for conducting the pulmonary diffusion capacity test. Such machines typically deliver a known quantity of a test gas with known concentrations of various components to a patient wherein the test gas includes a small non-harmful and specific initial concentration of carbon monoxide, along with a tracer gas that does not cross the lung membrane and allows a user to calculate dilution of the test gas in the lungs. Some DLco testing machines require that the person being tested take several breaths from the machine before the testing begins to start programming. Other machines provide only a single test breath. Subsequently to receiving a test breath from the machine, the patient breathes out or exhales the gas that has been received from the machine back into the machine after a specific elapsed period of time. The machine then performs certain analysis on the test gas exhaled by the patient, normally to determine fairly accurately the exhaled concentration of carbon monoxide which will be less than the inhaled concentration since some will cross the lung membrane.
The present invention is not directed to the machine that delivers the test gas to the patient and receives the subsequent exhaled gas for analysis, but rather to an apparatus for testing the machine to insure that it is correctly analyzing the exhaled gasses. In order to check the calibration of the testing machine to determine whether it is accurate in measuring the carbon monoxide concentration in the exhaled gasses, it is important to mimic the testing procedure as much as possible in order to locate and identify problems not only with the carbon monoxide analyzer, but with the procedure for delivering the gas to the carbon monoxide analyzer.
While simply delivering a gas stream of a predetermined concentration of carbon monoxide to the carbon monoxide analyzer of the machine allows a technician to determine whether or not the machine can accurately determine the carbon monoxide concentration, such a test does not take into account other factors which may affect the analyzed carbon monoxide concentration when the test is run in a true medical environment with a patient. For example, it may be found that the testing machine is not correctly receiving the exhaled gas from the patient or that the tubing to the testing machine is too long and contains too much extraneous gas which then dilutes the gas sample, so as to provide an inaccurate analysis.
Consequently, it is important for the calibration apparatus to both provide a standardized gas of known carbon monoxide concentration, but also to provide the gas in a manner that is as realistic to the actual use with a patient as possible in order to insure that other factors do not cause the tester to incorrectly analyze the carbon monoxide gas concentration.
A DLco calibration syringe apparatus is provided for calibrating and insuring the accuracy of pulmonary testing machines that allow a patient to inhale a gas containing a low percentage of carbon monoxide and then, subsequently, receive back and analyze the exhaled gas from the patient to determine the percentage concentration of carbon monoxide after a given time period or sequence of events. The calibration apparatus includes a pair of adjacent syringes joined on one end by a gas flow passage that also communicates during use with the DLco testing machine. Flow through the gas passageway is controlled by a multi-position valve. The first of the syringes includes a piston slideably mounted in a chamber that is joined to the gas flow pathway and which receives a quantity of gas from the testing machine upon proper positioning of the valve. The receipt of the gas from the testing machine by the first syringe is designed to simulate inhalation of a breath by a patient of a predetermined amount of gas having a preselected concentration of carbon monoxide. The first syringe is calibrated by volume and may be utilized to simulate taking and delivering several breaths from the machine in a pre-breathing mode required by certain of such machines.
The second syringe also includes a cylinder with a piston mounted therein so as to form a chamber in communication with the gas flow passageway. The second chamber is filled with a quantity of test gas wherein the percentage concentration of at least the carbon monoxide in the test gas is known and, preferably, all of the concentrations of the components of the test gas are known with some precision. Normally, the remainder of the gasses in the test gas will include an inert gas that generally does not cross the lung membrane, such as methane, neon or helium and will have a concentration of oxygen similar to ambient air. The test gas may have other gasses in concentrations found in typical exhaled breaths. After a given period of time, for example, ten seconds, or after a series of events occurs, the valve in the gas passageway is routed so as to communicate the second syringe with the test machine and the syringe is operated by a user to discharge the test gas therein into the testing machine.
The apparatus also includes a fill system joined with a test gas sample tank that can be selectively flow connected with the second syringe chamber by the person administering the test, as well as a bleed valve to allow some of the test gas to pass through the gas passageway to purge other gasses positioned therein and a relief valve to prevent the second syringe from being over-pressurized.
Therefore, the objects of the present invention are: to provide a syringe calibration apparatus for calibrating DLco testing machines comprising a pair of closely mounted syringes having internal pistons slideably mounted within a cylinder to form a variable volume chamber therein; to provide such an apparatus wherein the internal chambers of the syringes are joined by a flow controllable gas passageway with each other and with the testing machine during usage; to provide such an apparatus wherein the first of the syringes is sized and shaped to receive a preselected volume of gas from the testing machine and the second syringe is sized and shaped to return a preselected volume of test gas to the testing machine with a preselected concentration of carbon monoxide; to provide such an apparatus wherein the gas flow passageway has relatively very little dead space between the second syringe and the test machine; to provide such an apparatus wherein the gas flow passageway provides a purge valve to allow purging of the passageway with test gas prior to usage; to provide such an apparatus wherein the first syringe chamber is operably joined with a supply of test gas under control of a fill valve; to provide such an apparatus wherein the syringe that receives gas from the test machine can be set to receive varying amounts of gas and designed to allow an operator to return the gas from the cylinder to the machine in certain pre-breathing modes; and to provide such a calibration apparatus which is relatively inexpensive to produce, easy to use, and especially well adapted for the intended usage thereof.
Other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention.
The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof.